This invention relates generally to an automated centrifuge and, more specifically, to a centrifuge with inner and outer concentric rings of tubes which can be automatically controlled in repeated centrifuging, decanting, pouring, washing and mixing operations.
Centrifuges having inner and outer rings or banks of tubes are known in the art. See U.S. Pat. No. 4,190,530; Forsythe et al. Also, the use of a static resilient member to frictionally engage tubes during a portion of their rotation in a centrifuge to enhance the mixing action is known. See U.S. Pat. No. 3,401,876, Lucas. However, prior centrifuge systems have failed to provide the automatic operation required for many relatively complicated laboratory applications.
One typical centrifuging procedure which requires multiple steps is the DNA plasmid "mini-prep". Plasmids are short, circular rings of DNA that reside in bacteria such as E. coli. They are used frequently as tools in genetic engineering. By removing the plasmid from the bacterium, cleaving the ring at a certain point, inserting a different section of DNA, re-joining the ring and inserting the ring into another, "host", bacterium, the bacterium will "express" the genetic information contained in the inserted DNA section. Most often the presence of the new length of DNA will induce the bacterium to produce a compound or drug which is difficult to manufacture by conventional means.
The above procedure has usually been done in batches of thousands of bacteria and comprises the following steps:
1. The bacteria is grown overnight in Luria Broth in a tube and then centrifuged two minutes at 10,000 RPM.
2. The centrifuge is stopped, supernatant is decanted to waste.
3. The cells are resuspended by vortex action.
4. Lysis buffer is added to break open cells and then mixed.
5. Neutralization buffer is added and then mixed.
6. The tubes sit for 1-10 minutes.
7. The tubes are centrifuged for 10 minutes at 15,000 RPM.
8. The centrifuge is stopped and the supernatant decanted into a clean tube.
9. Alcohol is added to the supernatant to precipitate the plasmids and then mixed.
10. This mixture is then centrifuged for 3 minutes at 13,000 RPM.
11. The centrifuge is stopped and the supernatant decanted to waste.
12. The pellet containing plasmids is washed and then mixed to re-suspend.
Procedures of the above type are labor intensive, requiring dedicated operator attention and care to operate the centrifuge, pipette liquid into the tubes and decant from one tube into another. Operator skill varies from person to person, especially in the decanting operation, so reproducibility of the procedure varies accordingly. Efficient, costeffective automation of such procedures could insure reproducibility and free the operator for more productive tasks.